1. Field of the Invention
The present invention relates to an LED lighting tube and, more particularly, to an LED lighting tube compatible with an electronic ballast having a preheat current.
2. Description of Related Art
With reference to FIG. 2, a conventional fluorescent tube 60 is a gas-discharge lamp, and, accordingly, filaments 62 mounted in a tube 61 of the fluorescent tube 60 has to be heated to ionize gas in the tube 61 before the fluorescent tube 60 begins to glow.
In general, the fluorescent tube 60 has a first terminal L and a second terminal N respectively mounted on two ends of the fluorescent tube 60 and respectively connected to AC output terminals of an electronic ballast 70. The first terminal L has two electrode pins L1, L2 and the second terminal N has two electrode pins N1, N2. Two filaments 62 are mounted in the tube 61 and respectively connected in series between the electrode pins L1, L2 and between the electrode pins N1, N2. When the fluorescent tube 60 connected to a rapid start ballast or a program start ballast is turned on, the ballast produces preheat currents to the first terminal L and the second terminal N. After the preheat currents flow through and heat the filaments 62 to ionize the gas in the tube 61, the fluorescent tube 60 starts to glow.
Currently, an LED lighting tube has a structure of the first terminal L and the second terminal N of the fluorescent tube 60 in order to be compatible with a conventional fluorescent tube holder. An LED unit is mounted in the LED lighting tube and is used as a light source of the LED lighting tube. Two ends of the LED unit are respectively connected to the first terminal L and the second terminal N to obtain a power supply. However, the LED lighting tube does not have a structure of the filaments 62, such that there is no impedance (filaments 62) between the electrode pins L1, L2 of the first terminal L, and between the electrode pins N1, N2 of the second terminal N. Therefore, if the LED lighting tube is directly mounted in a fluorescent tube holder having a rapid start ballast or a program start ballast, the electronic ballast 70 produces short-circuit currents respectively to the electrode pins L1, L2 and to the electrode pins N1, N2 when the LED lighting tube is switched on. The electronic ballast 70 and the LED lighting tube may be damaged due to the short-circuit currents.